1. Field of the Invention
The present invention relates to an ink, particularly to an ink jet recording ink, and more particularly to an aqueous ink providing an image improved in discoloration and fading resistance in an indoor environment, an ink jet recording method utilizing the same, and an ink tank, a recording unit and an ink jet recording apparatus to be used therein.
2. Related Background Art
Images obtained by the ink jet recording have acquired so fine an image quality as to be comparable with a silver halide photograph, a representative of high image quality. Recently, in addition to the original image quality, preservation of such a fine image for a long period of time without deterioration has become a major concern for the user. In view of a prolonged storage of an image, fading with light is a major problem which has been tackled by selecting dyes of high light fastness. For example, as a dye for a cyan color ink, C.I. Direct Blue 199 or C.I. Direct Blue 86 is now employed.
The ink jet print as a “photograph” is often displayed in an indoor environment. In such a case, discoloration may occur within a short period in spite of usage of dyes having excellent light fastness. Such fading or discoloration in the indoor environment is caused by environmental gasses such as ozone, nitrogen oxide, sulfur oxide etc. in the air. It proceeds even when the print is scarcely exposed to the light, and takes place within a relatively short period particularly with coated paper employing an inorganic pigment for the coating layer.
Such a drawback is not solved with conventional dyes such as C.I. Direct Blue 199 or C.I. Direct Blue 86 having a sulfon group or a sulfonamide group introduced into the copper phthalocyanine for water solubility. In order to improve the gas resistance, various methods have been proposed as patent applications, such as introduction of substituents into the copper phthalocyanine skeleton different from C.I. Direct Blue 199 etc., and employment of a dye of another skeleton in combination with the conventional dyes. For example, Japanese Patent Application Laid-open No. 2002-105349A discloses, as a cyan dye compound for an ink jet ink with an improved gas resistance, a mixture of compounds obtainable by chlorosulfonating a copper phthalocyanine and then amidating using 2.5 moles or more of an amidating agent to 1 mole of the starting copper phthalocyanine, represented by the following formula (II): wherein M represents a proton, an alkali metal ion, an alkali earth metal ion, or an onium ion or an ammonium ion of an organic amine; m represents an integer from 1 to 4; n represents an integer from 1 to 3; and m+n is an integer from 1 to 4.
However, the present inventors have found that an ink jet ink containing such phthalocyanine dyes may reveal excellent gas resistance but have another drawback that an image formed with such an ink on a specific recording medium such as coating paper and glossy paper suffers from very poor water resistance and metallic luster called bronze phenomenon due to the coagulation of the dye on the recording medium.